Coreactive materials and methods for three-dimensional printing

ABSTRACT

Methods of printing a three-dimensional object using co-reactive components are disclosed. Thermosetting compositions for three-dimensional printing are also disclosed.

This application is a continuation of U.S. application Ser. No.16/269,277, filed on Feb. 6, 2019, which is a continuation of U.S.application Ser. No. 15/528,205, filed on May 19, 2017, issued as U.S.Pat. No. 10,253,195, which is a national stage entry ofPCT/US2015/062297, filed on Nov. 24, 2015, which claims the benefitunder 35 U.S.C. § 19(e) of U.S. Provisional Application No. 62/158,588,filed on May 8, 2015, and U.S. Application No. 62/083,472 filed on Nov.24, 2014, each of which is incorporated by reference in its entirety.

This invention was made with government support under Contract NumberDE-AC05-00OR22725 awarded by the U.S. Department of Energy and underCooperative Research and Development Agreement NFE-14-05242. Thegovernment has certain rights in the invention.

FIELD

The present invention relates to three-dimensional printing methods andcoreactive printing compositions, more particularly to the use ofthree-dimensional printing compositions comprising coreactivecomponents.

BACKGROUND

In three-dimensional (3D) printing, a composition is laid down insuccessive layers of material to build a structure from a series ofcross-sections of the structure. These layers may be produced, forexample, from liquid, powder, paper, or sheet material.

In certain cases, a 3D printing composition is a thermoplastic material,which is extruded through a heated nozzle on to a platform and thenozzle moved with respect to the platform, successively building uplayers of thermoplastic material to form a 3D object. After beingextruded from the nozzle, the thermoplastic material rapidly cools.Depending in part on the temperature of the underlying thermoplasticlayer, the overlying thermoplastic layer may or may not adhere well tothe underlying thermoplastic layer. Furthermore, differential thermalexpansion can cause stress to be built up in the finished object therebydiminishing the integrity of the object.

SUMMARY

Embodiments of the present disclosure include methods ofthree-dimensional printing of an object by forming an object using acoreactive printing composition, such as polyurea composition, that isproduced from a mixture of at least two coreactive components havingcoreactive functional groups wherein at least one of the coreactivecomponents comprises a saturated functional group. Also included withinthe scope of the present disclosure is printed three-dimensional objectsformed from layers of a coreactive printing composition, such as apolyurea composition, produced from at least two coreactive components.

According to the present invention, compositions for three-dimensionalprinting comprise: a first component comprising a first functionalgroup; and a second component comprising a second functional group,wherein the second functional group is reactive with the firstfunctional group; and wherein at least one of the first functional groupand the second functional group comprises a saturated functional group.

According to the present invention, compositions for three-dimensionalprinting comprise: a first component comprising a first functionalgroup; and a second component comprising a second functional group,wherein, the first component comprises a polyamine and the secondcomponent comprises a polyisocyanate; the first component comprises apolyalkenyl compound and the second component comprises a polythiol; thefirst component comprises a Michael addition acceptor and the secondcomponent comprises a Michael addition donor; or a combination of any ofthe foregoing; wherein the composition is characterized by a shearstorage modulus G′ and a shear loss modulus G″, wherein, the initialG″/G′ ratio is less than 2; the initial G′ is greater than 1,500 Pa; theG′ at 6 minutes is greater than 500,000 Pa; and the G″ at 6 minutesafter mixing is greater than 400,000 Pa; wherein, the shear storagemodulus G′ and the shear loss modulus G″ are measured using a rheometerwith a gap from 1 mm to 2 mm, with a 25 mm-diameter parallel platespindle, an oscillation frequency of 1 Hz and amplitude of 0.3%, andwith a rheometer plate temperature of 25° C.

According to the present invention, compositions comprise: a firstcomponent comprising a first functional group; and a second componentcomprising a second functional group, wherein, the first componentcomprises a polyamine and the second component comprises apolyisocyanate; the first component comprises a polyalkenyl compound andthe second component comprises a polythiol; the first componentcomprises a Michael addition acceptor and the second component comprisesa Michael addition donor; or a combination of any of the foregoing;wherein the composition is characterized by: a viscosity less than 30cP; a surface tension of 30 mN/m to 50 nM/m; a contact angle on glass ofless than 20 degrees; and a contact angle on polyethylene terephthalateof less than 40 degrees.

According to the present invention, three-dimensional object can beformed using a composition provided by the present disclosure.

According to the present invention, methods of three-dimensionalprinting an object comprise: extruding a first component comprising afirst functional group and a second component comprising a secondfunctional group, wherein, the second functional group is reactive withthe first functional group; and at least one of the first functionalgroup and the second functional group comprises a saturated functionalgroup; and building a three-dimensional printed object.

According to the present invention, methods of three-dimensionalprinting an object comprise: depositing by inkjet printing a firstreactive component comprising a first functional group; depositing byinkjet printing a second component comprising a second functional group;wherein, the second functional group is reactive with the firstfunctional group; and at least one of the first functional group and thesecond functional group comprises a saturated functional group; andbuilding a three-dimensional printed object.

According to the present invention, three-dimensional objects can beformed using a method provided by the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only. Thedrawings are not intended to limit the scope of the present disclosure.

FIG. 1 is a graph showing the dynamic modulus (G′ vs. G″) of polyureacompositions that did not satisfy desired build criteria.

FIG. 2 is a graph showing the dynamic modulus (G′ vs. G″) of polyureacompositions that met desired build criteria.

DESCRIPTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the invention are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard variation foundin their respective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

The use of the singular includes the plural and plural encompassessingular, unless specifically stated otherwise. In addition, the use of“or” means “and/or” unless specifically stated otherwise, even though“and/or” may be explicitly used in certain instances.

The term “polymer” is meant to include prepolymer, homopolymer,copolymer, and oligomer.

Embodiments of the present disclosure are directed to the production ofstructural objects using three-dimensional printing. A three-dimensionalobject may be produced by forming successive portions or layers of anobject by depositing at least two coreactive components onto a substrateand thereafter depositing additional portions or layers of the objectover the underlying deposited portion or layer. Layers are successivelydeposited to build the 3D printed object. The coreactive components canbe mixed and then deposited or can be deposited separately. Whendeposited separately, the components can be deposited simultaneously,sequentially, or both simultaneously and sequentially.

Deposition and similar terms refer to the application of a printingmaterial comprising a thermosetting or coreactive composition and/or itsreactive components onto a substrate (for a first portion of the object)or onto previously deposited portions or layers of the object. Eachcoreactive component may include monomers, prepolymers, adducts,polymers, and/or crosslinking agents, which can chemically react withthe constituents of the other coreactive component.

By “portions of an object” is meant subunits of an object, such aslayers of an object. The layers may be on successive horizontal parallelplanes. The portions may be parallel planes of the deposited material orbeads of the deposited material produced as discreet droplets or as acontinuous stream of material. The at least two coreactive componentsmay each be provided neat or may also include a solvent (organic and/orwater) and/or other additives as described below. Coreactive componentsprovided by the present disclosure may be substantially free of solvent.By substantially free is meant less than about 5 wt %, less than about 4wt %, less than about 2 wt %, or less than 1 wt % of solvent, where wt %is based on the total weight of a composition.

The at least two coreactive components may be mixed together andsubsequently deposited as a mixture of coreactive components that reactto form portions of the object. For example, the two coreactivecomponents may be mixed together and deposited as a mixture ofcoreactive components that react to form the thermosetting compositionby delivery of at least two separate streams of the coreactivecomponents into a mixer such as a static mixer to produce a singlestream that is then deposited. The coreactive components may be at leastpartially reacted by the time a composition comprising the reactionmixture is deposited. The deposited reaction mixture may react at leastin part after deposition and may also react with previously depositedportions and/or subsequently deposited portions of the object such asunderlying layers or overlying layers of the object.

Alternatively, the two coreactive components may be deposited separatelyfrom each other to react upon deposition to form the portions of theobject. For example, the two coreactive components may be depositedseparately such as by using an inkjet printing system whereby thecoreactive components are deposited overlying each other and/or adjacentto each other in sufficient proximity so the two reactive components mayreact to form the portions of the object. As another example, in anextrusion, rather than being homogeneous, a cross-sectional profile ofthe extrusion may be inhomogeneous such that different portions of thecross-sectional profile may have one of the two coreactive componentsand/or may contain a mixture of the two coreactive components in adifferent molar and/or equivalents ratio.

Furthermore, throughout a 3D-printed object, different parts of theobject may be formed using different proportions of the two coreactivecomponents such that different parts of an object may be characterizedby different material properties. For example, some parts of an objectmay be rigid and other parts of an object may be flexible.

It will be appreciated that the viscosity, reaction rate, and otherproperties of the coreactive components may be adjusted to control theflow of the coreactive components and/or the thermosetting compositionssuch that the deposited portions and/or the object achieves and retainsa desired structural integrity following deposition. The viscosity ofthe coreactive components may be adjusted by the inclusion of a solvent,or the coreactive components may be substantially free of a solvent orcompletely free of a solvent. The viscosity of the coreactive componentsmay be adjusted by the inclusion of a filler, or the coreactivecomponents may be substantially free of a filler or completely free of afiller. The viscosity of the coreactive components may be adjusted byusing components having lower or higher molecular weight. For example, acoreactive component may comprise a prepolymer, a monomer, or acombination of a prepolymer and a monomer. The viscosity of thecoreactive components may be adjusted by changing the depositiontemperature. The coreactive components may have a viscosity andtemperature profile that may be adjusted for the particular depositionmethod used, such as mixing prior to deposition and/or ink-jetting. Theviscosity may be affected by the composition of the coreactivecomponents themselves and/or may be controlled by the inclusion ofrheology modifiers as described herein.

It can be desirable that the viscosity and/or the reaction rate be suchthat following deposition of the coreactive components the compositionretains an intended shape. For example, if the viscosity is too lowand/or the reaction rate is too slow a deposited composition may flow ina way the compromises the desired shape of the finished object.Similarly, if the viscosity is too high and/or the reaction rate is toofast, the desired shape may be compromised.

For example, the coreactive components that are deposited together mayeach have a viscosity at 25° C. and a shear rate at 0.1 s⁻¹ from 5,000centipoise (cP) to 5,000,000 cP, from 50,000 cP to 4,000,000 cP, or from200,000 cP to 2,000,000 cP. The coreactive components that are depositedtogether may each have a viscosity at 25° C. and a shear rate at 1,000s⁻¹ from 50 centipoise (cP) to 50,000 cP, from 100 cP to 20,000 cP, orfrom 200 to 10,000 cP. Viscosity values can be measured using an AntonPaar MCR 301 or 302 rheometer with a gap from 1 mm to 2 mm.

Coreactive components that are ink jetted or otherwise depositedseparately from each other (not mixed before deposition) may have aviscosity at 25° C. of at least 1 cP, at least 5 cP, or at least 10 cP.The separately deposited coreactive components may have a viscosity at25° C. that is no more than 20 cP, no more than 30 cP, no more than 40cP, no more than 50 cP, no more than 75 cP, no more than 100 cP, or nomore than 120 cP.

The rate of interlayer crosslinking between successive and adjacentlayers of a deposited object can be controlled to facilitate interlayerreaction and thereby improve the interlayer strength. The rate ofinterlayer crosslinking can be controlled, for example, by adjusting thetime between deposition of successive layers, adjusting the temperature,adjusting the concentration of a catalyst, and/or adjusting thecomponents of the composition such as the amount of monomer andprepolymer. A deposited layer may be homogeneous or a deposited layermay be inhomogeneous. For an inhomogeneous layer, a cross-section of thelayer may have different chemical compositions. For example to improveinterlayer adhesion, a part of a layer may have an excess of a certaincoreactive functionality that can then react with an excess of acoreactive functionality of an overlying layer. Similarly, to improveinterlayer adhesion, a lower part of a layer may have an excess of acertain coreactive functionality that can then react with an excess of acoreactive functionality of an underlying layer. To improve interlayeradhesion, a tie coating, film, or layer may be applied or deposited overa deposited layer prior to or during deposition of an overlying layer.

The coreactive components may include a first component having at leasttwo functional groups per molecule (referred to as the “A” functionalgroups) and a second component having at least two functional groups permolecule (referred to as the “B” functional groups), where the Afunctional groups and the B functional groups are coreactive with eachother, are different from each other, and at least one of the twocoreactive components includes a saturated functional group.

A “saturated functional group” refers to a functional group of componentcoreactive component that does not include an unsaturated reactivegroup, although there may be unsaturation in other (non-reactive)portions of the compound of the coreactive component. An example of asaturated group includes thiol groups and an example of an unsaturatedgroup includes alkenyl and acrylate groups. Examples of saturatedfunctional groups include thiol, hydroxyl, primary amine, secondaryamine, and epoxy groups. In certain compositions, a saturated functionalgroup can be a thiol, a primary amine, a secondary amine, or acombination of any of the foregoing. In certain compositions, asaturated functional group can be a thiol, a primary amine, a secondaryamine, an epoxy, or a combination of any of the foregoing. Examples ofunsaturated functional groups include alkenyl groups, activatedunsaturated groups such as acrylate, maleic, or fumaric acid groups,isocyanate groups, acyclic carbonate groups, acetoacetate groups,carboxylic acid groups, Michael acceptor groups, vinyl ether groups,(meth)acrylate groups, and malonate groups.

Compositions provided by the present disclosure can comprise a firstcomponent comprising a first functional group, and a second componentcomprising a second functional group, wherein the second functionalgroup is reactive with the first functional group, and both of thefunctional groups do not comprise ethylenically unsaturated groups.Examples of ethylenically unsaturated groups include (meth)acrylategroups, Michael acceptor groups, and vinyl ether groups.

In certain compositions provided by the present disclosure the firstcomponent and the second component do not include a polyisocyanate and apolyol.

B functional groups may be capable of reacting with the A functionalgroups at moderate temperature such as less than 140° C., less than 100°C., less than 60° C., less than 50° C., less than 40° C., less than 30°C., or less than 25° C. The A and B functional groups may react togetherat room temperature such as 20° C. One or both of the coreactivecomponents may have on average more than two reactive groups permolecule, in which case the mixture of coreactive components comprises athermosetting composition. Suitable coreactive functional groups aredescribed, for example, in Noomen, Proceedings of the XIIIthInternational Conference in Organic Coatings Science and Technology,Athens, 1987, page 251; and in Tillet et al., Progress in PolymerScience 36 (2011), 191-217, which is incorporated by reference in itsentirety. The reaction between the A groups and the B groups may notinvolve the elimination of a by-product. Such reactions are oftenreferred to as addition reactions. Examples of suitable coreactivefunctional groups A and B are listed in Table 1.

TABLE 1 Functional Groups. Functional Groups A Functional Groups BCarboxylic acid Epoxy Activated unsaturated groups Primary or secondaryamine such as acrylate, maleic or fumaric Isocyanate Primary orsecondary amine Isocyanate Hydroxyl Cyclic carbonate Primary orsecondary amine Acetoacetate Primary or secondary amine Epoxy Primary orsecondary amine Thiol Alkenyl Thiol Vinyl ether Thiol (Meth)acrylateActivated unsaturated groups Malonate such as acrylate or maleic

A first coreactive component may include compounds having more than onetype of functional group A, and the second coreactive component mayinclude components having more than one type of functional group B, suchthat a 3D-printing material can comprise at least two sets of coreactiveA and B groups, wherein at least one coreactive component has afunctional group that is saturated. For example, a first coreactivecomponent may have hydroxyl groups and secondary amine groups (i.e. atleast two different functional groups) and the second coreactivecomponent may have isocyanate groups. One or both of the coreactivecomponents may optionally comprise a catalyst for the reaction betweenthe A groups and the B groups. The A groups and the B groups may beattached to any suitable compound such as a monomer and/or a prepolymer.Optionally, the A groups and the B groups may be attached to anoligomer, polymer, or prepolymer such as polyester, polyurethane, oracrylic oligomer, polymer, or prepolymer. In general, monomers refer tocompounds without repeating units in the backbone, and can becharacterized, for example, by a molecular weight less than 600 Daltons,less than 500 Daltons, or less than 400 Daltons. In general, aprepolymer refers to a compound having repeat units in backbone and canbe characterized, for example, by a molecular weight from 1,000 Daltonsto 20,000 Daltons, from 1,000 Daltons to 10,000 Daltons, or from 2,000Daltons to 5,000 Daltons.

The functional groups A and B may be terminal groups and/or pendentgroups. A coreactive component can have a functionality of two or afunctionality greater than two, such as a functionality from 2 to 6.Each functional group of a coreactive component can be the same orcertain functional groups of a coreactive component can be different.For example, a coreactive component can have more than one differenttype of functional group reactive with an isocyanate, such as a primaryamine group, a secondary amine group, or a hydroxyl group.

In a composition comprising at least two coreactive component, the firstcomponent can comprise a polyamine and the second component can comprisea polyisocyanate; the first component can comprise a polyalkenylcompound and the second component can comprise a polythiol; a the firstcomponent can comprise a Michael addition acceptor and the secondcomponent can comprise a Michael addition donor; or a combination of anyof the foregoing; In a composition comprising at least two coreactivecomponents, the first component can comprise an isocyanate-functionalprepolymer; and the second functional group can comprise a primaryamine, a secondary amine, a hydroxyl, or a combination of any of theforegoing.

A composition for three-dimensional printing can comprise a firstcomponent comprising a first functional group, and a second componentcomprising a second functional group, wherein the first and secondfunctional groups are reactive with each other, and at least one of thefirst functional group and the second functional group comprise asaturated functional group. One of the first and second functionalgroups may be an unsaturated functional group, or both the first andsecond functional groups may be a saturated functional group. Both thefirst functional group and the second functional groups are notunsaturated functional groups. A composition provided by the presentdisclosure may contain additional coreactive components, which maycomprise saturated and/or unsaturated functional groups.

The coreactive functional groups can react to form covalent bonds. Thereaction between the coreactive functional groups can be catalyzed by acatalyst. In certain compositions, the reaction between the coreactivefunctional groups does not involve a free-radical initiated reaction.Compositions provided by the present disclosure may be thermosetcompositions.

Compositions provided by the present disclosure may include twocoreactive components or more than two coreactive components. A reactivecomponent can comprise a combination of reactive components having thesame functional group, such as a combination of monomers and prepolymershaving the same functional group. An additional coreactive component cancomprise a compound having a different functional group reactive with afirst functional group or the second functional group. An additionalcoreactive component can impart an additional property to thecomposition. For example, the reaction rate of the additional coreactivecomponent with one of the other coreactive components may be rapid andthereby facilitate the ability of a deposited layer to maintain adesired shape before the other components fully cure.

The first component and the second component can be combined in asuitable ratio to form a curable composition. For example, thefunctional Group A to functional Group B equivalent ratio of a curablecomposition can be from 1:1 to 1.5:1, from 1:1 to 1.45:1, from 1: to3:1, from 1.2:1 to 1.5:1, or from 1.2:1 to 1.4:1. A suitable functionalGroup A to functional Group B equivalent ratio of a curable compositioncan be, for example, from 2:1 to 1:2, from 1.5:1 to 1:1.5, or from 1.1:1to 1:1.1.

Compositions provided by the present disclosure can include one or bothof the coreactive components such that the ratio of coreactivecomponents in one portion of the object differs from the ratio ofcoreactive components in another part of the object. In this manner,portions of an object may have differing final compositions. Thedifferent compositions may differ by the weight percent of thecoreactive compositions, the equivalent ratio of reactive monomers orreactants within the coreactive compositions, the type and/or level offiller, the crosslinking density, and/or properties such as glasstransition temperature. Accordingly, one portion of an object producedin the three-dimensional printing may have different material propertiessuch as different chemical, physical, thermal, or material propertiesthan those of another portion of the three-dimensional object.

In addition, one portion of an object may partially react with at leastsome other coreactive components in an adjacent portion of the object.Such reaction may occur during deposition and/or after the coreactivecomponents are deposited in each adjacent portion, whereby thecoreactive components react in part within each adjacent portion and thecoreactive components between adjacent portions react. In this manner,the deposited portions of an object may be covalently bound together asthe coreactive compositions react between the portions of the object,thereby increasing the physical and structural integrity of thethree-dimensional object. For example, unreacted isocyanate and/or aminegroups present on the surface of an underlying deposited layer, canreact with unreacted groups of a subsequently deposited layer. Thisincreases the strength/integrity of the object by providing reactionbetween layers of deposited material, in addition to reaction within thesame layer.

A printed three-dimensional object can include layers formed from athermosetting or coreactive composition, such as a polyurea composition,that is produced from at least two printed coreactive components andwhich may be crosslinked. In the case of polyurea, one of the coreactivecomponents may include an isocyanate-functional prepolymer or oligomerand another coreactive component may include an amine such as a primaryor secondary amine The isocyanate-functional coreactive components mayfurther include isocyanate-functional monomers. The amine containingcoreactive component may further include another reactant withfunctional groups reactive with the isocyanate-functional prepolymer,oligomer, and/or monomer such as hydroxyl groups. Adjacent portions of aprinted three-dimensional object may be reacted with some of thecoreactive compositions in one or more adjacent portions.

For a polyurea composition, the coreactive components may include anisocyanate-functional component that may include polyisocyanatemonomers, prepolymers, oligomers, adducts, polymers, or a blend ofpolyisocyanates. A prepolymer can be a polyisocyanate which ispre-reacted with a sufficient amount of polyamine(s) or otherisocyanate-reactive components such as one or more polyols, so thatreactive isocyanate sites on the polyisocyanate remain in theisocyanate-functional prepolymer.

Suitable monomeric polyisocyanates include, for example, isophoronediisocyanate (IPDI), which is3,3,5-trimethyl-5-isocyanato-methyl-cyclohexyl isocyanate; hydrogenateddiisocyanates such as cyclohexylene diisocyanate,4,4′-methylenedicyclohexyl diisocyanate (H₁₂MDI); mixed aralkyldiisocyanates such as tetramethylxylyl diisocyanates,OCN—C(—CH₃)₂—C₆H₄C(CH₃)₂—NCO; and polymethylene isocyanates such as1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate,1,6-hexamethylene diisocyanate (HMDI), 1,7-heptamethylene diisocyanate,2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate, 1,10-decamethylenediisocyanate and 2-methyl-1,5-pentamethylene diisocyanate.

Aliphatic isocyanates are particularly useful in producingthree-dimensional polyurea objects that are resistant to degradation byUV light. However, in other circumstances, less costly aromaticpolyisocyanates may be used when durability is not of significantconcern. Examples of monomeric aromatic polyisocyanates includephenylene diisocyanate, toluene diisocyanate (TDI), xylene diisocyanate,1,5-naphthalene diisocyanate, chlorophenylene 2,4-diisocyanate,bitoluene diisocyanate, dianisidine diisocyanate, tolidine diisocyanateand alkylated benzene diisocyanates generally; methylene-interruptedaromatic diisocyanates such as methylenediphenyl diisocyanate,especially the 4,4′-isomer (MDI) including alkylated analogs such as3,3′-dimethyl-4,4′-diphenylmethane diisocyanate and polymericmethylenediphenyl diisocyanate.

Suitable polyisocyanates also include polyisocyanates prepared fromdimers and trimers of diisocyanate monomers. Dimers and trimers ofdiisocyanate monomers can be prepared, for example, by methods describedin U.S. Pat. No. 5,777,061 at column 3, line 44 through column 4, line40, which is incorporated by reference in its entirety. Dimers andtrimers of diisocyanate monomers may contain linkages selected fromisocyanurate, uretdione, biuret, allophanate and combinations thereof,such as Desmodur® N3600, Desmodur® CP2410, and Desmodur® N3400,available from Bayer Material Science.

A polyisocyanate can also comprise a polyisocyanate prepolymer. Forexample, a polyisocyanate can include an isocyanate-terminated polyetherdiol, an extended polyether diol, or a combination thereof. An extendedpolyether diol refers to a polyether diol that has been reacted with anexcess of a diisocyanate resulting in an isocyanate-terminated polyetherprepolymer with increased molecular weight and urethane linkages in thebackbone. Examples of polyether diols include Terathane® polyether diolssuch as Terathane® 200 and Terathane® 650 available from Invista or thePolyTHF® polyether diols available from BASF. Isocyanate-terminatedpolyether prepolymers can be prepared by reacting a diisocyanate and apolyether diol as described in U.S. Application Publication No.2013/0344340, which is incorporated by reference in its entirety. Thenumber average molecular weight of an extended isocyanate-terminatedprepolymer can be, for example, from 250 Daltons to 10,000 Daltons, orfrom 500 Daltons to 7,500 Daltons.

A polyisocyanate can include a difunctional isocyanate, a trifunctionalisocyanate, a difunctional isocyanate-terminated prepolymer, an extendeddifunctional isocyanate-terminated prepolymer, or a combination of anyof the foregoing.

The amine-functional coreactive component used to produce athree-dimensional polyurea object may include primary and/or secondaryamines or mixtures thereof. The amines may be monoamines, or polyaminessuch as diamines, triamines, higher polyamines and/or mixtures thereof.The amines also may be aromatic or aliphatic such as cycloaliphatics.Examples of suitable aliphatic polyamines include, ethylene diamine,1,2-diaminopropane, 1,4-diaminobutane, 1,3-diaminopentane,1,6-diaminohexane, 2-methyl-1,5-pentane diamine,2,5-diamino-2,5-dimethylhexane, 2,2,4- and/or2,4,4-trimethyl-1,6-diamino-hexane, 1,11-diaminoundecane,1,12-diaminododecane, 1,3- and/or 1,4- cyclohexane diamine,1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane, 2,4- and/or2,6-hexahydrotolulene diamine, 2,4′- and/or 4,4′-diamino-dicyclohexylmethane, 5-amino-1,3,3-trimethylcyclohexanemethylamine(isophoronediamine), 1,3-cyclohexanebis(methylamine) (1,3 BAC), and3,3′-dialkyl-4,4′-diaminodicyclohexyl methanes (such as3,3′-dimethyl-4,4′-diaminodicyclohexyl methane and3,3′-diethyl-4,4′-diaminodicyclohexyl methane), 2,4- and/or2,6-diaminotoluene and 2,4′- and/or 4,4′-diaminodiphenyl methane, ormixtures thereof.

Suitable secondary amines include acrylates and methacrylate-modifiedamines By “acrylate and methacrylate modified amines” includes bothmono- and poly-acrylate modified amines as well as acrylate ormethacrylate modified mono- or poly-amines Acrylate or methacrylatemodified amines can include aliphatic amines.

A secondary amine may include an aliphatic amine, such as acycloaliphatic diamine Such amines are available commercially fromHuntsman Corporation (Houston, Tex.) under the designation of JEFFLINK™such as JEFFLINK™ 754. The amine may be provided as an amine-functionalresin. Such amine-functional resins may be a relatively low viscosity,amine-functional resins suitable for use in the formulation of highsolids polyurea three-dimensional objects. An amine-functional resin maycomprise an ester of an organic acid, for example, an asparticester-based amine-functional reactive resin that is compatible withisocyanates; e.g., one that is solvent-free. An example of suchpolyaspartic esters is the derivative of diethyl maleate and1,5-diamino-2-methylpentane, available commercially from BayerCorporation. PA under the trade name DESMOPHEN™ NH1220. Other suitablecompounds containing aspartate groups may be employed as well.

An amine-functional coreactive component also may include high molecularweight primary amines, such as polyoxyalkyleneamines.Polyoxyalkyleneamines contain two or more primary amino groups attachedto a backbone, derived, for example, from propylene oxide, ethyleneoxide, or a mixture thereof. Examples of such amines include thoseavailable under the designation JEFFAMINE™ from Huntsman Corporation.Such amines can have a molecular weight from 200 Daltons to 7,500Daltons, such as, for example, JEFFAMINE™ D-230, D-400, D-2000, T-403and T-5000.

An amine-functional co-reactive component may also include an aliphaticsecondary amine such as Clearlink® 1000, available from Dor-KetalChemicals, LLC.

An amine-functional coreactive component can comprise anamine-functional aspartic acid ester, a polyoxyalkylene primary amine,an aliphatic secondary amine, or a combination of any of the foregoing.

For a polyurea formed from coreactive components comprising anisocyanate and a (meth)acrylate amine reaction product of a monoamineand poly(meth)acrylate, the term “(meth)acrylate” denotes both theacrylate and the corresponding (meth)acrylate. The poly(meth)acrylatemay be any suitable poly(meth)acrylate and mixtures thereof. Apoly(meth)acrylate can include a di(meth)acrylate, a poly(meth)acrylatecan comprise tri(meth)acrylate, or a poly(meth) acrylate can includetetra(meth)acrylate. Suitable di(meth)acrylates include, for example,ethylene glycol, di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate,1,4-butanediol di(meth)acrylate, 2,3-dimethylpropane1,3-di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, propylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate,tetrapropylene glycol di(meth)acrylate, ethoxylated hexanedioldi(meth)acrylate, propoxylated hexanediol di(meth)acrylate, neopentylglycol di(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate,hexylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,polyethylene glycol di(meth)acrylate, polybutadiene di(meth)acrylate,thiodiethyleneglycol di(meth)acrylate, trimethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, alkoxylatedhexanediol di(meth)acrylate, alkoxyolated neopentyl glycoldi(meth)acrylate, pentanediol di(meth)acrylate, cyclohexane dimethanoldi(meth)acrylate, ethoxylated bis-phenol A di(meth)acrylate, andmixtures of any of the foregoing. Examples of tri and higher(meth)acrylates include glycerol tri(meth)acrylate, trimethylolpropanetri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate,propoxylated trimethylolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylatedpentaerythritol tetra(meth)acrylate, propoxylated pentaerythritoltetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Othersuitable poly(meth)acrylate oligomers include (meth)acrylate ofepoxidized soya oil and urethane acrylates of polyisocyanates andhydroxyalkyl (meth)acrylates. Mixtures of poly(meth)acrylate monomersmay also be used, including mixtures of mono, di, tri, and/or tetra(meth)acrylate.

Other suitable poly(meth)acrylates include urethane (meth)acrylates suchas those formed from the reaction of hydroxy-functional (meth)acrylatewith a polyisocyanate or with an isocyanate-functional adduct of apolyisocyanate and a polyol or a polyamine Suitable hydroxy-functional(meth)acrylates include 2-hydroxyethyl, 1-methyl-2-hydroxyethyl,2-hydroxypropyl, 2-hydroxybutyl, 4-hydroxybutyl, and the like. Suitablepolyisocyanates include, for example, any of the monomeric or oligomericisocyanates, or isocyanate prepolymers disclosed herein.

A thermosetting or coreactive composition provided by the presentdisclosure can be based on thiol-ene chemistry. For example, athermosetting composition provided by the present invention havingthiol-ene functionality may include a polyene coreactive componentcomprising compounds or prepolymers having terminal and/or pendentolefinic double bonds, such as terminal alkenyl groups. Examples of suchcompounds include (meth)acrylic-functional (meth)acrylic copolymers,epoxy acrylates such as epoxy resin (meth)acrylates (such as thereaction product of bisphenol A diglycidyl ether and acrylic acid),polyester (meth)acrylates, polyether (meth)acrylates, polyurethane(meth)acrylates, amino (meth)acrylates, silicone (meth)acrylates, andmelamine (meth)acrylates.

Examples of suitable polyurethane (meth)acrylates include reactionproducts of polyisocyanates such as 1,6-hexamethylene diisocyanateand/or isophorone diisocyanate including isocyanurate and biuretderivatives thereof with hydroxyalkyl (meth)acrylates such ashydroxyethyl (meth)acrylate and/or hydroxypropyl (meth)acrylate.Examples of suitable polyester (meth)acrylates are the reaction productsof (meth)acrylic acid or anhydride with polyols, such as dials, trialsand tetraols, including alkylated polyols, such as propoxylated diolsand trials. Examples of suitable polyols include 1,4-butane diol,1,6-hexane dial, neopentyl glycol, trimethylol propane, pentaerythritoland propoxylated 1,6-hexane diol. Examples of suitable polyester(meth)acrylates include glycerol tri(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, andpentaerythritol tetra(meth)acrylate. Mixtures of polyurethane(meth)acrylates, and polyester (meth)acrylates may be used.

In addition to (meth)acrylates, (meth)allyl compounds or prepolymers maybe used either alone or in combination with (meth)acrylates. Examples of(meth)allyl compounds include polyallyl ethers such as the diallyl etherof 1,4-butane diol and the allyl ether of trimethylol propane. Examplesof other (meth)allyl compounds include polyurethanes containing(meth)allyl groups. For example, reaction products of polyisocyanatessuch as 1,6-hexamethylene diisocyanate and/or isophorone diisocyanateincluding isocyanurate and biuret derivatives thereof withhydroxy-functional allyl ethers, such as the monoallyl ether of1,4-butane diol and the diallylether of trimethylol propane can be used.

Isocyanate functionality may be incorporated into a coreactive componentin a number of ways. The polyurethane (meth)acrylate or the polyurethane(meth)allyl compound may be prepared in a manner such that the reactionproduct contains unreacted isocyanate groups. For example, theabove-mentioned reaction product of 1,6-hexamethylene diisocyanateand/or isophorone diisocyanate with hydroxyethyl (meth)acrylate and/orhydroxypropyl (meth)acrylate are reacted in an NCO/OH equivalent ratioof greater than 1. Alternately, such reaction products may be preparedsuch that they are isocyanate free, i.e., NCO/OH equivalent ratio equalto or less than 1, and a separate isocyanate compound such as apolyisocyanate may be included in the coreactive component.

A polythiol coreactive component refers to polyfunctional compoundscontaining two or more thiol-functional groups (—SH). Suitablepolythiol-functional compounds include polythiols having at least twothiol groups including monomers and prepolymers. A polythiol may haveether linkages (—O—), thioether linkages (—S—), including polysulfidelinkages (—S_(x)—), where x is at least 2, such as from 2 to 4, andcombinations of such linkages.

Examples of suitable polythiols include compounds of the formulaR¹—(SH)_(n), where R¹ is a polyvalent organic moiety and n is an integerof at least 2, such as from 2 to 6.

Examples of suitable polythiols include esters of thiol-containing acidsformed by reacting a thiol-containing acid of formula HS—R²—COOH whereR² is an organic moiety with a polyhydroxy compounds of the structureR₃—(OH)_(n) where R³ is an organic moiety and n is at least 2, such asfrom 2 to 6. These components may be reacted under suitable conditionsto give polythiols having the general structure R³—(OC(O)—R²—SH)_(n)wherein R², R³ and n are as defined above.

Examples of thiol-containing acids include thioglycolic acid(HS—CH₂COOH), α-mercaptopropionic acid (HS—CH(CH₃)—COOH) andβ-mercaptopropionic acid (HS—CH₂CH₂COCH) with poly hydroxy compoundssuch as glycols, triols, tetraols, pentaols, hexaols, and mixturesthereof. Other suitable polythiols include ethylene glycolbis(thioglycolate), ethylene glycol bis(β-mercaptopropionate),trimethylolpropane tris (thioglycolate), trimethylolpropane tris(β-mercaptopropionate), pentaerythritol tetrakis (thioglycolate) andpentaerythritol tetrakis (β-mercaptopropionate), and mixtures thereof.

Certain thermosetting compositions provided by the present disclosuremay employ Michael addition reactive components. The reactive componentsmay include primary amine-functional components and acrylate, maleic, orfumaric-functional components. Compounds that are useful primaryamine-functional components include polyoxyalkyleneamines containing twoor more primary amine groups attached to a backbone, derived, forexample, from propylene oxide, ethylene oxide, or a mixture thereof.Examples of such amines include those available under the designationJEFFAMINE™ from Huntsman Corporation. Such amines can have a molecularweight ranging from 200 Daltons to 7500 Daltons, such as, for example,JEFFAMINE™ D-230, D-400, D-2000, T-403, and T-5000. Compounds useful asacrylate functional components include the acrylate functionalcomponents listed previously as embodiments of (poly)methacrylate.Compounds useful as maleic or fumaric components include polyestersprepared from maleic anhydride, maleic acid, fumaric acid, or theircorresponding C₁₋₆ alkyl esters.

A Michael acceptor group refers to an activated alkenyl group such as analkenyl group proximate to an electron-withdrawing group such as aketone, nitro, halo, nitrile, carbonyl, or nitro group. Examples ofMichael acceptor groups include vinyl ketone, vinyl sulfone, quinone,enamine, ketimine, aldimine, oxazolidine, acrylate, acrylate esters,acrylonitrile, acrylamide, maleimide, alkylmethacrylates, vinylphosphonates, and vinyl pyridines.

Suitable examples of catalysts for Michael addition chemistries includetributylphosphine, triisobutylphosphine, tri-tertiary-butylphosphine,trioctyl phosphine, tris(2,4,4-trimethylpentyl)phosphine,tricyclopentylphosphine, tricyclohexalphosphine, tri-n-octylphosphine,tri-n-dodecylphosphine, triphenyl phosphine, and dimethyl phenylphosphine.

Thermosetting compositions used in producing three-dimensional objectscan include various additives such as rheology modifiers (e.g., silicaor other fillers), flow control agents, plasticizers, stabilizers,wetting agents, dispersing auxiliaries, deformers, and adhesionpromoters. In addition, three-dimensional printing of a thermosettingcomposition can include deposition of a thermosetting composition withina mold to provide temporary structural integrity to the object duringthe printing process.

Because the thermosetting compositions can have a low viscosity comparedto thermoplastic compositions it is possible to use high fillerconcentrations. The high filler concentrations can be used to modify theproperties of the finished object such as the mechanical, thermal,and/or electrical properties of the finished object. Thus, the use ofhigh filler concentrations facilitated by the use of three-dimensionalthermosetting compositions can greatly expand the design possibilitiesof three-dimensional printing. Furthermore, thermosetting compositionscan be provided having superior solvent and chemical resistance.

Examples of suitable fillers include fumed silica such as Cabosil® TS720available from Cabot Corporation and precipitated silica such asLo-Vel®™ or Hi Sil® silicas available from PPG Industries. A curablecomposition provided by the present disclosure can comprise, forexample, from 1 wt % to 40 wt % filler, from 1 wt % to 30 wt % filler,from 1 wt % to 25 wt % filler, from 5 wt % to 25 wt % filler, or from 10wt % to 20 wt % filler, where wt % is based on the total weight of thecurable composition. A filler may be included in the A component of atwo-part system, may be included in the B part of a two-componentsystem, or a filler may be included in both the A part and the B part.

A filler can be a low density filler characterized by, for example, aspecific gravity less than 0.7, less than 0.3, or less than 0.1. Use ofa low density filler can provide a three-dimensional printed objecthaving a low specific gravity, such as from 0.8 to 1, or from 0.7 to0.9.

A filler can be an electrically-conductive filler and can be used toimpart electrically conductivity and/or EMI/RFI shielding effectivenessto a three-dimensional printed object. For example, an electricallyconductive printed object can be characterized by a sheet resistanceless than 0.5 Ω/cm² or less 0.15 Ω/cm². For example, an electricallyconductive printed object can provide effective EMI/RFI over a frequencyrange from 1 MHz to 18 GHz, or a subrange between 1 MHz to 18 GHz.

Suitable fillers also include magnetic fillers and opaque fillers.

Three-dimensional printed objects can be fabricated using thecompositions provided by the present disclosure. A three-dimensionalprinted object can be fabricated by deposited successive layers of acompositions comprising coreactive components. The compositions can bedeposited, for example, using extrusion or using inkjet printingtechniques.

Extrusion of coreactive components is well known. The coreactivecomponents can be mixed in a barrel head pushed under pressure through asuitably shaped nozzle. The extruded composition or extrusion can becharacterized by a cross-sectional profile. The cross-sectional profilecan be characterized by a constant ratio the coreactive components or bya variable ratio of the coreactive components, where the ratio can referto the mole % ratio of the coreactive components, by the equivalentsratio of the functional groups, the wt % ratio of the reactivecomponents, or other useful ratio. An inhomogeneous composition acrossthe cross-sectional profile of an extrusion can be useful to impartdifferent properties to different parts of the profile. For example, itmay be useful to impart solvent resistance or electrically conductiveproperties to the outer portion of a profile. To facilitate adhesionbetween adjacent or adjoining layers such as underlying or overlyinglayers, it may be useful to include an excess of one or more of thecoreactive functional groups. For example, an top surface or a portionof a top surface of a layer may have an excess of a first coreactivefunctional group, and a bottom surface or a portion of a bottom surfaceof an overlying layer may have an excess of a second coreactivefunctional group, where the first and second coreactive functionalgroups are reactive with each other. In this way, formation of covalentbonding between the adjoining layers is facilitated and the physicalintegrity of a finished three-dimensional printed object can beincreased.

The rate of the curing reaction between the coreactive components canalso be controlled such that the reaction is not complete when asubsequent layer is deposited on an underlying layer. In this way,coreactive components of an overlying layer can react with thecoreactive components of an underlying layer to increase the strengthbetween layers. Coreactive thermoset materials with a high degree ofcrosslinking can also be used to provide high solvent and chemicalresistance to the finished part.

The ability of an extruded curable composition to maintain structuralintegrity and support an overlying layer of the composition wasquantified by correlating the dynamic modulus of the curable compositionand the desired properties. Desired properties, also referred to asbuild criteria, include the ability to maintain the shape of a depositedlayer, the ability to support one or more overlying layers, and theability to adhere or co-react with an adjacent layer. Theviscoelasticity of a curable composition can be determined using arotational rheometer to measure the shear storage modulus G′ and theshear loss modulus G″. For example, the dynamic modulus of polyureacompositions that did not meet the build criteria are shown in FIG. 1and the dynamic modulus of polyurea compositions that met the buildcriteria are shown in FIG. 2 . In FIGS. 1 and 2 , the initial G′ andG″of a curable composition immediately after mixing is shown by the opensquares and the G′ and G″ 6 minutes after mixing is shown by the solidcircles. A line connects the initial and 6-minute measures for aparticular coreactive composition. A G′ of 1,500 Pa is shown by thesolid vertical line, and a G′ of 1,000,000 Pa is shown by the dashedvertical line. A G″ of 600,000 Pa is shown by the dashed horizontalline. Coreactive compositions meeting three-dimensional printing buildcriteria can exhibit the following properties: (1) an initial G″/G′ratio less than 2; (2) an initial G′ greater than 1,500 Pa; (3) a 6 minG′ greater than 500,000 Pa; and (4) a 6 min G″ greater than 400,000 Pa.Coreactive compositions meeting three-dimensional printing buildcriteria can exhibit the following properties: (1) an initial G″/G′ratio less than 1.5; (2) an initial G′ greater than 2,000 Pa; (3) a 6min G′ greater than 10⁶ Pa; and (4) a 6 min G″ greater than 600,000 Pa.The initial G′ and initial G″ refers to the shear storage and shear lossmodulus, respectively, immediately after combining the A-functional andB-functional components, such as an isocyanate-functional A componentand an amine-functional B component, and the 6 min G′ and 6 min G″ referto the shear storage and shear loss modulus, respectively, 6 minutesafter the A and B components are combined. The values for the shearstorage modulus G′ and the shear loss modulus G″ can be measured usingan Anton Paar MCR 301 or 302 rheometer with a gap set to 1 mm, with a 25mm-diameter parallel plate spindle, and an oscillation frequency of 1 Hzand amplitude of 0.3%. The tests can be performed under ambientconditions with the temperature of the rheometer plate set to be 25° C.

Three-dimensional objects printed according to methods provided by thepresent disclosure provide benefits over previous 3D printed objects inboth the process for producing the object and in the properties of finalobject. For example, the deposition methods may not require any use ofadded heat, therefore avoiding the creation of stress buildup in thefinished object during cooling as occurs with three-dimensional printingof thermoplastic materials. The coreactive compositions provided by thepresent disclosure can have sufficiently low viscosity that thecompositions may be pumped and printed quickly and accurately. By usingcoreactive compositions that react fast and remain in place followingdeposition, improved control over the shape and dimensions of a printedobject may be realized. In addition, the coreactive compositionsprovided by the present disclosure may include materials that provideadditional properties to the object such as magnetic or conductiveincluding electrical and/or thermally conductive, properties, andstrength. Strengthening components include, for example, carbon fiber,glass fiber, and graphene. Colorants such as pigments or dyes can alsobe included in a printing composition. For coreactive compositions thatcrosslink quickly, strength in the printed object allows for rapidaddition of further layers on top of the previously printed portion ofthe object. Another benefit of the disclosed materials and methods isstrength as provided in the “z direction” of the printed object, wherethe x and y direction are the general planes of the building of thethree-dimensional object. Traditional three-dimensional printingprovides minimal adhesion between layers of the printed object,particularly when thermoplastic materials are used. By providingmaterial that forms covalent crosslinks between successive layers, thefinal printed object can have increased strength in the z direction.

The use of low viscosity coreactive or thermoset compositions canfacilitate deposition at room temperature thereby avoiding the hightemperature print heads characteristic of thermoplasticthree-dimensional printing apparatus. The use of thermosetting materialscan facilitate the use of simple and light weight print heads that canbe moved rapidly and precisely and can further simplify the variousdrive mechanisms.

Depending in part on control of the rheology profile and cure rate ofthe thermosetting compositions, it is possible to rapidly build partswith high structural integrity. The structural strength between adjacentlayers can also facilitate the ability to construct shapes that overhangan underlying layer.

Three-dimensional printed objects can also be fabricated using inkjetprinting. Inkjet printing three-dimensional printed objects aregenerally known in the art. In inkjet printing methods the coreactivecomponents may be deposited sequentially and/or simultaneously. The atleast two coreactive can be deposited using separate nozzles. Thecoreactive components can be deposited on top of each other and/oradjacent to each other. For inkjet printing, a composition can becharacterized by a viscosity less than 30 cP; a surface tension of 30mN/m to 50 nM/m; a contact angle on glass of less than 20 degrees; and acontact angle on polyethylene terephthalate of less than 40 degrees. Forinkjet printing the viscosity of the deposited composition can be fromabout 10 cP to about 30 cP, from about 10 cP to about 20 cP, or fromabout 5 cP to about 15 cP.

The at least two coreactive components can be deposited from a singlenozzle. In such cases the coreactive components can be mixed anddeposited before the curing reaction significantly proceeds, or thecoreactive components may have, for example, a sufficiently slow curingrate that they remain in liquid form following mixing. The slowlyreacting components can be deposited and a catalyst can then bedeposited from a separate nozzle to initiate the curing reaction betweenthe two coreactive components. Rather than be deposited as largedroplets, the coreactive components can be deposited as a spray.Deposition in the form of a spray can facilitate the ability of the twocoreactive components to mix prior to deposition. Because reactivethermoset compositions can have low viscosities, compared tothermoplastic compositions, deposition using sprays can be facilitated.

It should be understood that, where not mutually exclusive, the variousfeatures of the embodiments of the present disclosure described, shownand/or claimed herein may be used in combination with each other. Inaddition, the following Examples are presented to demonstrate thegeneral principles of the methods and compositions provided by thepresent disclosure. All amounts listed are described in parts by weight,unless otherwise indicated. The invention should not be considered aslimited to the specific Examples presented.

EXAMPLES Example 1 Rheology Characterization

The rheology of three-dimensional printing formulations was determinedusing an Anton Paar 301 or 302 rheometer. Two-component (A pack: amine;B pack: isocyanate) samples were mixed using either a dual-channelsyringe pump (Kd Scientific) or a hand mixing gun (Nordson), and thenimmediately deposited onto the rheometer to fill the sample gap (1 mL to2 mL). A disposable sample plate (Anton Paar, Cat. No 4847) was placedon the rheometer and used as the bottom plate in the measurements. Adisposable parallel plate spindle with a diameter of 25 mm (PP25) wasused for the measurements. The spindle was brought toward the sampleimmediately after loading, with the gap set at 1 mm. An oscillationmeasurement (frequency 1 Hz, amplitude 0.3%) was then applied.Rheological parameters (G′, G″, tan δ, |δ*|) were recorded over time.The tests were performed under ambient condition with the temperature ofthe rheometer plate set to be 25° C. The polyurea formulations evaluatedare provided in Table 2.

TABLE 2 A pack B pack Particle Particule NCO/NH Amine Particle contentIsocyanate Particle Particle Equivalent Formulation Component(s) type(wt %) Component(s) type (wt % Ratio A Desmonphen ® None 0 Desmodur ® XPNone 0 1.42 NH1220¹ 2410⁴ B Desmophen ® Cabosil ® 2 Desmodur ® XPCabosil ® 2 1.42 NH1220 TS720⁹ 2410 TS720 C Desmophen ® Cabosil ® 4Desmodur ® XP Cabosil ® 4 1.42 NH1220 TS720 2410 TS720 D 75 partsCabosil ® 5 90 parts PTMEG None 0 1.25 Jeffamine ® TS720 2000/IPDIT5000²/25 Prepolymer⁵, 10 parts parts of Clearlink ® PTMEG650/IPDI 1000³Prepolymer⁶ E 70 parts PPG 5 80 parts PTMEG None 0 1.42 Jeffamine ®precipitated 2000/IPDI T5000/30 Silica¹⁰ Prepolymer, 20 parts parts ofPTMEG Clearlink ® 650/IPDI 1000 Prepolymer F 55 parts None 0 60 partsPTMEG None 0 1 Jeffamine ® 2000/IPDI T5000/45 Prepolymer, 20 parts partsof PTMEG Clearlink ® 650/IPDI NH1220 Prepolymer G Desmophen ® Cabosil ®5 Desmodur ® XP Cabosil ® 5 1.42 NH1220 TS720 2410 TS720 H 60 parts PPG24 80 parts PTMEG None 0 1 Jeffamine ® precipitated 2000/IPDI T5000/40Silica Prepolymer, 20 parts parts of PTMEG Clearlink ® 650/IPDI 1000Prepolymer I 64 parts PPG 24 60 parts PTMEG None 0 1.42 Jeffamine ®precipitated 2000/IPDI T5000/36 Silica Prepolymer, 40 parts 650/IPDIClearlink ® Prepolymer 1000 J 47 parts PPG 24 60 parts None 0 1Jeffamine ® precipitated PTMEG2000/IP T5000/53 Silica DI Prepolymer,parts 40 parts of Clearlink ® PTMEG 1000 650/IPDI Prepolymer¹Desmophen ® NH1220, amine-functional aspartic acid ester, availablefrom Bayer Corporation. ²Jeffamine ® T5000, polyoxyalkylene primaryamine of approximately 5000 MW, available from Huntsman Corporation.³Clearlink ® 1000, aliphatic secondary amine, available from Dorf-KetalChemicals, LLC. ⁴Desmodur ® XP 2410, an asymmetric trimer ofhexamethylene diisocyanate, available from Bayer Material Science.⁵PTMEG 2000/IPDI prepolymer, reaction product of isophorone diisocyanateand TERATHANE ™ 2000⁷. ⁶PTMEG 650/IPDI prepolymer, reaction product ofisophorone diisocyanate and TERATHANE ™ 650⁸, as disclosed in U.S.Application Publication No. 2013/0344340, paragraph [0181]. ⁷TERATHANE ™2000, polythioether diol of approximately 2000 molecular weight,available from Invista. ⁸TERATHANE ™ 650, polythioether diol ofapproximately 650 molecular weight, available from Invista. ⁹Cabosil ®T5720, fumed silica available from Cabot Corporation. ¹⁰Lo-Vel ™ 27available from PPG Industries, Inc.

Graphs showing the dynamic modulus of the deposited polyurea exhibitingBuild 0 capability is provided in FIG. 1 and exhibiting Build 4capability is provided in FIG. 2 . Build Capability refers to asubjective assessment of the ability of a composition to produce asuccessful three-dimensional printed object. Criteria used to assessBuild capability include the ability to mechanically support overlyinglayers, the ability to maintain the deposited shape and dimensions, andthe ability to adhere or bond to adjacent layers. A value of 0represents unacceptable build capability and a value of 5 representsexcellent build capability.

The values for which tan δ (G′=G″) is 1 is shown as a diagonal line. Forvalues of tan δ greater than 1, the material has a stronger inelasticcomponent and for values of tan δ less than 1, the material has astronger elastic component. The measurements indicated by the opensquares were obtained immediately after the material was deposited onthe rheometer (t=0). The measurements indicated by the solid circleswere obtained 6 minutes after deposition and when the material hadpartially cured. Lines connect the measurements for on the sameformulation.

It was empirically determined that materials having a shear storagemodulus G′ and shear loss modulus G″ equal to or greater than 10⁶ Pawere sufficiently strong to support overlying build layers and couldsufficiently adhere to adjacent layers. This area is represented by thebox in the upper right hand corner of the dynamic modulus plot. It wasalso determined empirically that modulus values that provided asuccessful build included:

-   -   (1) a value of G″/G′ less than 1.5;    -   (2) an initial shear storage modulus G′ greater than 2,000 Pa;    -   (3) a 6 min G′ greater than 1,000,000 Pa; and    -   (4) a 6 min G″ greater than 600,000 Pa.        The initial conditions are represented by values of G′ and G″        below the tan δ line and to the left of the vertical line        representing G′ greater than 600,000 Pa.

The moduli (shear storage modulus G′ and shear loss modulus G″) for eachof the polyurea formulations included in Table 2 is provided in Table 3.

In the examples, the build capability tests on the formulations shown inTable 2 were performed using a dual channel syringe pump, affixed with ahelical static mixer with a 2 mm orifice to dispense the formulationonto the substrate and build. The material was dispensed at a rate of 5mL/min to 15 mL/min with the volume ratio of the two components adjustedto achieve the stoichiometry listed in Table 3. To assess the buildcapability of each formulation, a cube with a base approximately 2.5cm×2.5 cm was built by hand. The build capability was rated on a scaleof 0 to 5 with 5 being the best. A build rating of 0 indicated that thematerial flowed extensively and a three dimensional structure was notproduced. A build rating of 4 indicated that many layers could beprinted without the cube collapsing or warping, but some limited reflowof the composition occurred after deposition. A 5 build rating indicatedthat many layers could be printed without the cube collapsing orwarping, with no reflow of the composition after deposition.

TABLE 3 Dynamic modulus parameters for the polyurea formulations inTable 2. G′ initial G′ initial G′ at 6 G″ at 6 G″/G′ Build Formulation(Pa) (Pa) min (Pa) min (Pa) (tan ) Capability A   389    1.351  463830 705530* 288 0 B   191    73.5  413000  871000*  2.60 0 C   701   11401020000* 1850000*  0.61* 0 D  25354  15005*  373470  288510  1.69 0 E 25038  16595*  661540  349840  1.51 0 F  46274  40721*  194260  136930 1.14* 0 G  5689.2   4304* 4515600* 3707700*  1.32* 4 H  323230  333310*2289900*  803550*  0.97* 4 I  269730  220640* 2116600* 1090300*  1.22* 4J 1512300 3757600* 5328400* 1655700*  0.40* 4

The values of the parameters meeting successful build criteria (1)-(4)are identified in Table 3 with an asterisk. Formulations G-J met each ofthe build criteria (1)-(4).

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A composition for three-dimensional printing,comprising: a first component comprising a first compound, wherein thefirst compound comprises at least one first functional group; and asecond component comprising a second compound, wherein the secondcompound comprises at least one second functional group, wherein the atleast one second functional group is reactive with the at least onefirst functional group; wherein at least one of the first functionalgroup and the second functional group comprises a saturated functionalgroup; wherein each of the first functional group and the secondfunctional group does not comprise an ethylenically unsaturated group;and wherein the composition comprises a filler comprising a specificgravity less than 0.7.
 2. The composition of claim 1, wherein thecomposition has a specific gravity from 0.8 to
 1. 3. The composition ofclaim 1, wherein the composition has a specific gravity from 0.7 to 0.9.4. The composition of claim 1, wherein the composition is characterizedby: a viscosity less than 30 cP; a surface tension of 30 mN/m to 50nM/m; a contact angle on glass of less than 20 degrees; and a contactangle on polyethylene terephthalate of less than 40 degrees.
 5. Thecomposition of claim 1, wherein each of the first component and thesecond component comprises less than 5 wt % solvent, wherein wt % isbased on the total weight of each of the respective coreactivecomponents.
 6. The composition of claim 1, wherein an equivalents ratioof the at least one first functional group to the at least one secondfunctional group is from 2:1 to 1:2.
 7. The composition of claim 1,wherein the first compound and the second compound are capable ofcoreacting at a temperature less than 30° C.
 8. The composition of claim1, wherein each of the first component and the second componentindependently comprises: a monomer having a molecular weight less than600 Daltons; a prepolymer having a molecular weight with a range from1,000 Daltons to 20,000 Daltons; or a combination thereof.
 9. Thecomposition of claim 1, wherein, the composition comprises an additionalcoreactive component, wherein the additional coreactive componentcomprises a compound comprising at least one third functional group,wherein the at least one third functional group is different than thefirst functional group and the second functional group; and the thirdfunctional group is reactive with the first functional group or thesecond functional group.
 10. The composition of claim 9, wherein areaction rate of the third functional group with the first functionalgroup or the second functional group is different than a reaction rateof the first functional group with the second functional group.
 11. Thecomposition of claim 1, wherein the composition comprises from 1 wt % to40 wt % of the filler.
 12. The composition of claim 1, wherein thefiller comprises an electrically conductive filler.
 13. The compositionof claim 1, wherein the filler comprises silica.
 14. The composition ofclaim 1, wherein the filler comprises a magnetic filler.
 15. Thecomposition of claim 1, wherein the composition comprises a colorant.16. The composition of claim 1, wherein the composition comprises carbonfiber, glass fiber, graphene, or a combination of any of the foregoing.17. The composition of claim 1, wherein the composition comprises anamount of an electrically conductive filler sufficient to imparteffective EMI/RFI resistance over a frequency range of 1 MHz to 18 GHzto a three-dimensional object.
 18. The composition of claim 1, whereinthe first component and the second component are mixed to form anextrusion comprising a cross-sectional profile.
 19. An object preparedfrom the composition of claim
 1. 20. The object of claim 19, wherein theobject has a specific gravity from 0.8 to
 1. 21. The object of claim 19,wherein the object has a specific gravity from 0.7 to 0.9.
 22. Theobject of claim 19, wherein the object comprises a shape that overhangsan underlying layer.
 23. A cured composition prepared from thecomposition of claim
 1. 24. An object comprising the cured compositionof claim 23.